A female Plains Wanderer protecting its nest at Terrick Terrick National Park: Photo John Childs
Article kindly provided by Dr David Baker-Gabb
The Plains-wanderer is a globally significant species
The nationally endangered Plains-wanderer Pedionomus torquatus is the sole member of a Family of birds, the Pedionomidae. Like the flightless ratites (eg Emu, Cassowary, Ostrich, Kiwi and Rhea), the Plains-wanderer is one of a handful of surviving representatives of an ancient avifauna that was once dispersed across the great southern Gondwana supercontinent before it began to drift apart c.100 million years ago. Consequently, the Plains-wanderer’s nearest, albeit distant, relatives are in South America.
A recently-published review of the world’s 9,993 recognised bird species asked which species can we least afford to lose in the current extinction crisis if maximum global avian evolutionary diversity is to be maintained? This review ranked the Plains-wanderer #1 among Australian birds and #4 in the world. This means that those land managers with Plains-wanderers on their properties have a globally significant responsibility and need to be supported accordingly.
Plains-wanderer breeding habits
The Plains-wanderer is unusual among birds in that the larger, more colourful female defends the territory. The more cryptically-coloured male does most of the incubation after the female has laid 3-5 eggs in a scrape on the ground in sparse native grassland. The male then does all of the rearing of the 2-4 chicks. This leaves the dominant female free to pair with a second male. Neighbouring territorial females usually remain c.400m apart and may occupy the same c.12ha territories in consecutive years so long as the grassland structure remains suitable for them.
Grassland structure is the key
Grassland structure rather than floristic composition is overwhelmingly the most important predictor of habitat use by Plains-wanderers. This consistent result has been determined by means of experiments with captive birds, radio-tracking of wild birds, and many thousands of kilometres of nocturnal surveys in sparse and dense grasslands over the last 30 years.
Short, sparse grasslands are required by Plains-wanderers because they feed by walking between well-spaced tussocks and picking up seeds and insects from the ground. Moreover, Plains-wanderers are not sufficiently strong flyers to be able evade aerial predators in flight and so they use their remarkably cryptic plumage for concealment. For this reason they will not venture within 200m of trees where hunting raptors commonly perch. For Plains-wanderers to evade ground predators, grasslands need to be low enough for the birds can detect them at a distance and then move stealthily between tussocks to keep well away from the predator. Plains-wanderers will stand on a grass tussock and stretch up to 15cm tall on tip-toes to observe a predator. Tall, dense grass hinders all of these essential activities, as does cultivation and severe overgrazing.
Cultivation has caused major population declines
Cultivation of lowland native grasslands in the 20th century removed c.99% of the Plains-wanderers’ prime habitat which occurred in coastal and sub-coastal south-eastern Australia. More than half of the records of Plains-wanderers in Australia prior to 1940 came from just one area: the plains west of Melbourne. Following cultivation, the number of records on the grassy plains west of Melbourne declined markedly, though 16 Plains-wanderers were recorded there in the 1980s and five in the last five years.
The Plains-wanderer’s two remaining strongholds are Victoria’s Northern Plains and the Riverina of New South Wales. They also occur in some localised inland arid areas in very low densities. The Riverina has been subjected to less cultivation than the Northern Plains where c.95% of the native grassland has been lost to cultivation and agricultural intensification. Cultivation is ongoing on Victoria’s Northern Plains, with 80% of grasslands where Plains-wanderers were located in the 1990s lost to cultivation within a decade, and some of what remains outside reserves lost in the last five years.
Many of the best of the remaining native grassland blocks on the Northern Plains have been acquired for reserves over the past 20 years, with the conservation of the nationally endangered Plains-wanderer as a key objective. This still leaves c.70% of potential habitat on the Northern Plains in private hands. Reserves played an important role in conserving Victoria’s Plains-wanderers during the 2002-09 droughts because, unlike much of the private land, they were not overgrazed at this time. Widespread overgrazing during past droughts has caused Plains-wanderer populations to decline by up to 75%.
Bush Tender and Reserves
In 2008, the ‘best of the rest’ Plains-wanderer habitat remaining in private ownership on the Northern Plains became the focus of the Victorian government’s multi-million dollar ‘Bush Tender’ program whereby landholders are paid to achieve biodiversity outcomes. Several landholders with good quality grasslands entered into five-year contracts that either restricted or prohibited grazing. This outlay resulted in reserves and private properties under Bush Tender contracts having the primary role in the conservation of the Plains-wanderer in Victoria. If the drought had continued this could have been a good scheme for Plains-wanderers. Instead, historically high rainfall was recorded for two years, commencing in mid-2010. Grassland biomass increased markedly and in the absence of a corresponding increase in grazing intensity the vegetation structure of nearly all grassland paddocks was profoundly altered. For over two years the red soil rises that are preferred habitat of Plains-wanderers supported a thick, tall sward of native grasses with very few inter-tussock spaces instead of a grassland characterised by a low, open structure with inter-tussock spaces dominated by herbs and forbs. There was also a much higher biomass of litter on the ground than usual. The Plains-wanderer population crashed by an unprecedented c.95% and has remained at these low levels to the present day. A similar decline occurred in the Plains-wanderer’s other stronghold, the NSW Riverina.
Inadequate management response
The Bush Tender scheme did not provide any financial or other support for monitoring of its impact on Plains-wanderers over its first five years of operation on the Northern Plains, despite requests to do so. Farmers’ concerns about the impact of the huge increase in grass biomass on threatened grassland flora and fauna in the face of inadequate or no grazing also went unheeded. DSE Bendigo supported monitoring of Plains-wanderers that demonstrated the significant, negative impact of the major change in grassland biomass on the birds, and only then was some limited ‘exceptional circumstances’ grazing permitted, but by then it was too little and too late for the Plains-wanderer.
There was also a massive increase in the biomass of grass on reserves and from historically high numbers in 2010, Plains-wanderer numbers plummeted there too and they have remained very low ever since. With so much grass available, farmers were not interested in agisting stock on reserves. Those sheep that were already on reserves were not concentrated in one or two paddocks to control the grass there, and so all paddocks became thoroughly overgrown. Nor were paddocks slashed to reduce biomass. Moreover, autumn burns planned to reduce the biomass on reserve paddocks generally failed to eventuate and so many reserve paddocks remain too dense for Plains-wanderers to this day.
The only places where Plains-wanderers have continued to reside in very low numbers during this recent wet period has been on a few private properties being grazed for production purposes. Plains-wanderers would have encountered high rainfall events and unfavourable conditions previously, including as recently as the mid 1970s. Historically, there would have been more native grassland remaining in the landscape spanning a larger range in habitat structure due to natural variation in soil type and local rainfall. Moreover, land use has changed markedly in the last two decades with more land now cropped and a much smaller national sheep flock, particularly in south-eastern Australia. In addition, large areas in northern Victoria are now in the national reserve system or have been under Bush Tender agreements that temporarily restrict stock grazing. Thus, the amount of habitat and grazing intensity during and immediately after the last “big wet” in the 1970s would have been substantially higher than today, which would have acted to counter the local effects of high biomass and reduced habitat suitability.
Plains-wanderers have recovered from lesser setbacks in the past and so monitoring to record any population recovery needs to continue. This monitoring needs to include any areas that are mechanically slashed or burnt to modify grassland structure.
A range of on-ground measures on both reserves and private land could help avoid major declines in Plains-wanderer populations in future. Domestic stock prefer to concentrate their grazing on areas of red soil occupied by Plains-wanderers and so such areas are often overgrazed before managers can achieve their desired level of grazing control over entire paddocks. Fencing to soil type, using traditional or electric fencing, would enable farmers and reserve managers to achieve better grassland management through rotational grazing, and to remove stock before Plains-wanderer habitat was overgrazed. During droughts incentives would need to be paid to farmers for excluding stock from Plains-wanderer habitat and feeding the stock hay or pellets that were at least equivalent to the value of the forage foregone. After very wet periods stock could be concentrated in fenced Plains-wanderer habitat on reserves and farms for longer to produce the grassland structure required. In this case a portable water source may be required if the fenced section does not have access to water.
To avoid detection by perched birds of prey, Plains-wanderers do not venture within 200m of small trees and large shrubs (2-5m), nor within 300m of trees >10m tall. Removing stands of planted gums and numerous scattered mature African boxthorns would instantly make available to Plains-wanderers >200ha of otherwise suitable habitat on the Northern Plains.
Many potential areas of Plains-wanderer habitat have never been surveyed. Vehicle-based nocturnal surveys for Plains-wanderers over vast areas of Australia’s inland plains are moderately expensive. Female Plains-wanderers have a distinctive call. The development and use of acoustic surveys using numerous, widely-distributed microphones and computer analysis of their recordings could be revolutionary.
In combination, implementing these actions should make a significant contribution towards the effective management and conservation of the Plains-wanderer, Australia’s most distinctive endangered bird.
Recent Plains Wanderer Update